Clues suggest N Korean sub behind warship attack

Tokyo: Experts say North Korea`s submarine fleet is technologically backward, prone to sinking or running aground, and all but useless outside its own coastal waters.

And yet many are asking: Could it have been responsible for the explosion that sank a South Korean warship in March? And if so, how could a sub have slipped through the defences of South Korea, which, with significant American backing, maintains a fleet far more sophisticated than its northern neighbour`s?

Evidence collected thus far indicates a torpedo hit the Cheonan, killing 46 sailors, and suspicion is growing that it was launched from a small North Korean submarine. That scenario would make it the most serious attack on the South Korean military since the peninsula`s war ended in a truce in 1953.

"While the North Korean submarine force reflects dated technology by Western standards, North Korean submarines during wartime would present significant challenges, particularly in coastal areas," according to the Arlington, Virginia-based Global Security think tank.

"North Korea has placed high priority on submarine construction programmes, which are ongoing despite its economic hardships."

Without witnesses or communications traffic to use as evidence, proving North Korea was behind the attack is difficult.

Still, teams conducting an intensive salvage and analysis mission are beginning to put the pieces together.

Officials say they know the 1,200-ton warship -- a small, lightly armed frigate that split in half while on patrol in waters near the Koreas` tense western maritime border – sank after a powerful external blast created a shock wave of the sort normally associated with a torpedo or mine.

South Korean media have reported that traces of the high explosive RDX have been found in the wreckage, which would also be consistent with a torpedo attack.

"It is plausible that the ship was hit by a torpedo," Joseph Bermudez, a North Korea military expert and senior analyst for the London-based Jane`s Information Group, said.

North Korean subs are not state-of-the-art. Instead, they underscore impoverished North Korea`s focus on "asymmetric" warfare -- the use of stealthy, relatively low-cost weapons that many a ragtag fighting force have proved can open up big holes in conventional defences.